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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

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Characteristic of colza and ravison oils, and of those of the other Crucifera
mentioned above, are their low saponification number (see Table XLIV)
and their content of eracic acid. By the determination of the saponification
number and essentially by certain tests on the fatty acids these oils may
be identified and their presence in mixtures with other oils detected. These
tests are as follows.1

1. The Tortelli and Fortini Tests on the Fatty Acids.—These
tests include 'the determinations of the melting point and iodine number of
the solid fatty acids and the critical solubility temperature of the sodium
soap of the liquid acids, these characters being especially influenced by
the presence of eracic acid. The solid and liquid fatty acids should first
be prepared (see a) and the determinations indicated then made (see b and c).

(a)  Preparation of the solid and liquid fatty acids.   20 grams of the
oil are saponified with alcoholic potash and the potassium soap converted
into the lead soap by the Tortelli and Ruggeri method (see General Methods,
18, i).    The lead soap, dried with filter-paper, is taken up with 80 c.c. of
ether, shaken well, heated for 20-30 minutes in a reflux apparatus with
occasional shaking and then cooled in water at 15° for an hour.   The ethereal
liquid is subsequently decanted through a filter into a separating funnel,
as little as possible of the solid residue being introduced on to the filter.
The residue is heated with 40 c.c. of ether in a reflux apparatus for 20 minutes,
cooled at 15° for an hour, and the whole then collected on the filter, the
filtrate passing into the separating funnel.   The flask and residue are washed
with 40 c.c. of ether.    This washed lead soap, insoluble in ether, is intro-
duced into another separating funnel by perforating the filter and washing
down with ether, of which 100 c.c. are used.

To each separating funnel 150 c.c. of 20% hydrochloric acid are added,
the funnel being thoroughly shaken and then left at rest until the ethereal
layer has separated well, the aqueous liquid and the lead chloride formed
being run off. This treatment is repeated with a second quantity of 100
c.c. of hydrochloric acid and if necessary with a third quantity. The two
ethereal solutions are then washed twice with 100-150 c.c. of water, care
being taken not to shake too vigorously. The ethereal solutions are finally
filtered through two pleated filter-papers into two glass dishes, from which
the solvent is evaporated at as low a temperature as possible. In one dish
the solid acids (from the lead salts insoluble in ether) and in the other the
liquid acids of the oil remain.

(b)  Tests on the solid acids.   The melting point is determined with a
bulb tube (see General Part, 4) and is taken as that temperature at which
the substance falls into the lower part of the bulb.   The iodine number is
determined by Hiibl's method.

The solid fatty acids of pure colza oil melt at 41-42° and have the iodine
number 62 : those of other seed oils and of olive oil melt at higher temperatures
and have lower iodine numbers (see" later).

(c)  Tests on the liquid acids.   The sodium soap cf these is prepared and

1 Use may also be made with advantage of Holde and Marcusson's method (Zeitschr.
filr angew. Chem., 1910, p. 1260), which is based on the solubility of erucic acid in
alcohol at a low temperature.I, p. 676), Luers (##, 1912, XXIV, p, 683), an4 Evers (Analyst,